The present invention relates generally to intramedullary nails for the fixation of bone fractures and, in particular, to intramedullary nails having an expandable portion for securely maintaining the nail within the medullary cavity of one of the fractured bone portions.
The use of intramedullary nailing for the fixation of bone fractures is well known. Such a procedure rejoins and reinforces the broken bone portions of a body limb and, in many instances, permits the functional rehabilitation of the limb within a relatively short time.
The earliest types of intramedullary nails consisted of a single diameter rod constructed of a non-corrosive material. Typically, the diameter of the nail was selected to correspond with the narrowest part of the medullary cavity of the bone into which the nail was to be inserted. Since the diameter of these nails was relatively thin throughout the length of the bone, the nails were usually not strong enough to take up the stresses originally carried by the bone. This problem was especially evident in larger bones such as, for example, the femur. Consequently, in these instances, the limb had to be immobilized for a relatively long period, which not only rendered the patient unfit for work during that time but also involved the danger of muscle atrophy and other ailments associated with prolonged convalescence.
In order to hasten the return of mobility of the damaged limb, it became necessary to use stronger nails. The use of a larger diameter nail was made possible by enlarging the medullary cavity by reaming the bone. Typically, such a nail was constructed with a uniform cross section throughout its entire length except for the front tip which was tapered inwardly to assist in the insertion of the nail through the bone marrow. However, the principal drawback of this type of nail is that the practice of enlarging the medullary cavity tends to weaken the shaft of the bone and reduce the blood supply to the fractured ends, thereby impeding the healing process.
Another problem associated with the above-described intramedullary nails is that, in some instances, the lateral support provided by the nail is very limited due to the construction of tubular bones. Typically, tubular bones have a longitudinally extending, marrow-containing cavity having a contour which converges in the central portion of the bone and then diverges in a longitudinal direction near the ends of the bone. Consequently, an intramedullary nail having a uniform cross section will typically only contact the inner wall of the medullary cavity of the bone only over a small region. Such a nail provides only limited lateral support between the fractured bone portions.
One approach to providing increased lateral support at the fracture was to use an intramedullary nail having an expandable end portion. Such a nail has a retracted diameter in the end portion which permits the nail to be inserted through the convergent portion of the medullary cavity, and thereafter expanded to engage the increased diameter inner wall of the divergent portion. Such expansion nails have resulted in increased lateral retention of the fractured bone portions but are relatively expensive and sometimes require complex devices to effect the expansion of the end portion. Typical examples of such prior art expandable nails are shown in U.S. Pat. Nos. 3,760,802, 3,530,854 and 4,091,806.